Optical information recording medium which uses diffraction grating

ABSTRACT

In an optical information recording medium of this invention, at least one cell including diffraction gratings is disposed on a planar substrate. This cell is divided into n (n is an integer of 2 or more) regions such that each divided region represents one binary data. To read information, light-receiving elements corresponding in number of the number n of divided regions of the cell are disposed to correspond to the respective divided regions. One incident light beam is caused to be incident on the cell. Diffracted light components emerging from the respective divided regions of the cell are received by the light-receiving elements, thereby reproducing data. Thus, information can be recorded at a very high density, and information can be read at a high speed.

TECHNICAL FIELD

The present invention relates to an optical information recording mediumfrom which information is optically reproduced and an informationreading method for the same and, more particularly, to an opticalinformation recording medium which uses diffraction gratings asinformation recording elements so that information can be recorded at avery high density and from which a plurality of pieces of informationare read at once simultaneously so that information can be read at ahigher speed, and an information reading method for the same.

BACKGROUND ART

Generally, optical recording has advantages in that, e.g., a recordingmedium and a head do not contact each other when compared to magneticrecording, and high-density recording can be performed. Various types ofmedia are known as optical recording media for optical recording, e.g.,a read-only medium, a write-once medium, and an erasable programmablemedium.

Optical recording media of these types have already been in practicaluse in various fields in the forms of, e.g., an optical recording disk(e.g., a CD, a CD-ROM, a CD-I, a laser disk, write-once and programmabledisks, and a magneto-optical disk) and an optical card (e.g., a ROMcard, write-once and programmable cards, and a magneto-optical card).

In a conventional read-only or write-once optical recording disk, alaser beam generated by a light source, e.g., a semiconductor laser, isfocused to form a spot having a diameter of 1 to 2 μm on the disksurface, and the surface state of the corresponding portion on the disksurface is detected by utilizing light reflected by the disk surface.

More specifically, when a pit is present, light is randomly reflected toreduce the intensity of the reflected light. When a pit is not present,light is reflected by a mirror surface. Data is read by utilizing adifference (intensity of light) between these two states.

In this case, however, a decrease in spot diameter of the laser lightbeam is limited to as small as about 1 to 2 μm, and it is impossible todecrease the spot diameter to be extremely smaller than this.

Accordingly, the information amount of the conventional opticalrecording disk is limited by the fact that one pit on the diskrepresents one piece of information and by the limited spot diameter ofthe laser light beam. As a result, information recording at a highdensity exceeding a certain limit cannot be performed.

DISCLOSURE OF INVENTION

It is the first object of the present invention to provide an opticalinformation recording medium which uses diffraction gratings asinformation recording elements so that information can be recorded at avery high density and from which a plurality of pieces of informationare read at once simultaneously so that information can be read at ahigher speed, and an information reading method for the same.

It is the second object of the present invention to provide an opticalinformation recording medium which uses diffraction gratings asinformation recording elements so that information can be recorded at avery high density, from which a plurality of pieces of information areread at once simultaneously so that information can be read at a higherspeed, and which can be produced in mass production with a goodformability at a low cost, and an information reading method for thesame.

It is the third object of the present invention to provide an opticalinformation recording medium which uses diffraction gratings asinformation recording elements so that information can be recorded at avery high density, from which a plurality of pieces of information areread at once simultaneously so that information can be read at a higherspeed, and which can improve a security effect, and an informationreading method for the same.

In order to achieve the first object, in an optical informationrecording medium according to the first aspect of the present invention,at least one cell comprising diffraction gratings is disposed on aplanar substrate, and the cell is divided into n (n is an integer of 2or more) regions such that each divided region represents one binarydata.

Particularly, a cell comprising diffraction gratings having at leasteither different inclinations or different grating pitches and formed inthe divided regions is used as the cell.

A cell comprising diffraction gratings which are obtained by aligningcurved gratings parallel to each other to have constant grating pitchesis used as the cell.

A cell comprising diffraction gratings which are obtained by aligningcurved gratings parallel to each other to have different grating pitchesis used as the cell.

A cell comprising diffraction gratings which are obtained by aligningconcentric circles at a predetermined gap is used as the cell, and thecell is divided into n regions by lines extending through the center ofthe concentric circles such that each divided region represents onebinary data.

A cell comprising diffraction gratings which are obtained by aligningconcentric circles at different gaps is used as the cell, and the cellis divided into n regions by lines extending through the center of theconcentric circles such that each divided region represents one binarydata.

Either a reflection type cell or a transmission type cell is used as thecell.

According to an information reading method for an optical informationrecording medium according to the first aspect of the present invention,light-receiving elements corresponding in number to a number n ofdivided regions of the cell are disposed to correspond to the dividedregions, and one incident light beam is caused to be incident on thecell, and diffracted light components emerging from the divided regionsof the cell are received by the light-receiving elements, therebyreproducing information.

Beam-like light is caused to be incident as the incident light.

In order to achieve the second object of the present invention, in anoptical information recording medium according to the second aspect ofthe present invention, which is formed by disposing at least one cellcomprising small diffraction gratings on a surface of a planarsubstrate, a ratio of a line width to a grating pitch of the diffractiongratings constituting the diffraction grating cell is appropriatelychanged based on first original data used for manufacturing a main bodyof the optical information recording medium, thereby recording firstdata.

A ratio of a line width to a grating pitch of the diffraction gratingsconstituting the diffraction grating cell is appropriately changed basedon first original data used for manufacturing a main body of the opticalinformation recording medium, thereby recording first data, and agrating pitch of the diffraction gratings constituting the diffractiongrating cell is appropriately changed based on second original data usedfor manufacturing the main body of the optical information recordingmedium, thereby recording second data.

A ratio of a line width to a grating pitch of the diffraction gratingsconstituting the diffraction grating cell is appropriately changed basedon first original data used for manufacturing a main body of the opticalinformation recording medium, thereby recording first data, and anazimuth angle of diffraction of the diffraction gratings constitutingthe diffraction grating cell is appropriately changed based on thirdoriginal data used for manufacturing the main body of the opticalinformation recording medium, thereby recording third data.

A ratio of a line width to a grating pitch of the diffraction gratingsconstituting the diffraction grating cell is appropriately changed basedon first original data used for manufacturing a main body of the opticalinformation recording medium, thereby recording first data, a gratingpitch of the diffraction gratings constituting the diffraction gratingcell is appropriately changed based on second original data used formanufacturing the main body of the optical information recording medium,thereby recording second data, and an azimuth angle of diffraction ofthe diffraction gratings constituting the diffraction grating cell isappropriately changed based on third original data used formanufacturing the main body of the optical information recording medium,thereby recording third data.

An intensity of diffracted light component is coded based on thefollowing equation as a ratio of the line width to the grating pitch ofthe diffraction gratings: ##EQU1## where η is the diffraction efficiency(a value of 0 to 1), r is the depth of the diffraction gratings, l isthe line width, d is the grating pitch, θ is the angle of incidence ofreproduced illumination light, and λ is the wavelength of thereproduction illumination light.

Either a reflection type cell or a transmission type cell is used as thecell.

According to an information reading method for an optical informationrecording medium of the second aspect of the present invention, at leastone light-receiving element is disposed, one incident light beam iscaused to be incident on the diffraction grating cell, and a diffractedlight component emerging from the diffraction grating cell is receivedby the light-receiving element, so that the first data is reproduced asa change in intensity of the diffracted light component.

A plurality of light-receiving elements are disposed, one incident lightbeam is caused to be incident on the diffraction grating cell, anddiffracted light components emerging from the diffraction grating cellare received by the light-receiving elements, so that the first data isreproduced as a change in intensity of the diffracted light componentand the second data is reproduced as a change in diffraction angle ofthe diffracted light component.

A plurality of light-receiving elements are disposed, one incident lightbeam is caused to be incident on the diffraction grating cell, anddiffracted light components emerging from the diffraction grating cellare received by the light-receiving elements, so that the first data isreproduced as a change in intensity of the diffracted light componentand the third data is reproduced as a change in exit direction of thediffracted light component.

A plurality of light-receiving elements are disposed, one incident lightbeam is caused to be incident on the diffraction grating cell, anddiffracted light components emerging from the diffraction grating cellare received by the light-receiving elements, so that the first data isreproduced as a change in intensity of the diffracted light component,the second data is reproduced as a change in diffraction angle of thediffracted light component, and the third data is reproduced as a changein exit direction of the diffracted light component.

Beam-like light is caused to be incident as the incident light.

In order to achieve the third object of the present invention accordingto the third aspect of the present invention, in an optical informationrecording medium formed by disposing at least one cell comprising smalldiffraction gratings on a surface of a planar substrate, the diffractiongrating cell is divided into a plurality of regions, in the samediffraction grating cell, the respective regions are constituted bydiffraction gratings having the same azimuth angle but different gratingpitches, a grating pitch of the diffraction gratings constituting atleast one of the respective regions is appropriately set based onoriginal data used for manufacturing a main body of the opticalinformation recording medium main body, thereby recording data.

The diffraction grating cell is divided into a plurality of regions, inthe same direction grating cell, the respective regions are constitutedby diffraction gratings having the same azimuth angle but differentgrating pitches, and shapes and positions of the respective regions areappropriately set in units of cells based on original data used ofmanufacturing a main body of the optical information recording medium,thereby recording data.

The diffraction grating cell is divided into a plurality of regions, inthe same diffraction grating cell, the respective regions areconstituted by diffraction gratings having the same azimuth angle butdifferent grating pitches, a grating pitch of the diffraction gratingsconstituting at least one of the respective regions is appropriate setbase on first original data used for manufacturing a main body of theoptical information recording medium, thereby recording first data, andshapes and positions of the respective regions are appropriately setbased on the second original data used for manufacturing the main bodyof the optical information recording medium main body, thereby recordingsecond data.

Particularly, the grating pitch of the diffraction gratings and an areaof the region are set such that a wavelength and the ratio of anintensity of a diffracted light component emerging from each region ofthe same diffraction grating cell corresponds to the color of one pointon a chromaticity digram from each cell.

A plurality of the diffraction grating cells are disposed, and azimuthangles of the diffraction gratings constituting the diffraction gratingcells are changed between the cells, thereby recording the third data.

Either a reflection type diffraction grating cell or a transmission typediffraction grating cell is used as the diffraction grating cell.

According to an information reading method for an optical informationrecording medium of the third aspect of the present invention, aplurality of light-receiving elements are disposed, one incident lightbeam is caused to be incident on the diffraction grating cell, anddiffracted light components emerging from the diffraction grating cellare received by the light-receiving elements, so that the data isreproduced as a change in diffraction angle of the diffracted lightcomponent of each region of the diffraction grating cell.

At least one light-receiving element is disposed, one incident lightbeam is caused to be incident on the diffraction grating cell, and adiffracted light component emerging from the diffraction grating cell isreceived by the light-receiving element, so that the data is reproducedas a spatial distribution of the diffracted light component in eachregion of the diffraction grating cell.

Furthermore, a plurality of light-receiving elements are disposed, oneincident light beam is caused to be incident on the diffraction gratingcell, and diffracted light components emerging from the diffractiongrating cell are received by the light-receiving elements, so that thefirst and second data are reproduced as a diffraction angle and aspatial distribution of the diffracted light component of each region inthe diffraction grating cell.

Particularly, in an information reading method for the above opticalinformation recording medium, a plurality of the light-receivingelements are disposed, and changes in spatial distribution of thediffracted light components received by the light-receiving elements arecompared with each other, thereby determining validity of reproduceddata.

Beam-like light is caused to be incident as the incident light.

Therefore, according to the information recording method for the opticalinformation recording medium of the first aspect of the presentinvention, a cell comprising the diffraction gratings is divided intotwo or more regions and each divided region represents one binary data,thereby recording a plurality of data in one cell.

According to the information reading method for the optical informationrecording medium of the first aspect of the present invention, wheninformation is to be read, one incident light beam is caused to beincident on the cell, and data is reproduced by receiving by diffractedlight components emerging from the respective divided regions of thecell by the respective light-receiving elements, thereby reproducing aplurality of data at once simultaneously.

According to the optical information recording medium of the secondaspect of the present invention, the ratio of the line width to thegrating pitch of the diffraction gratings constituting the diffractiongrating cell is approximately changed based on the first original dataused for manufacturing the main body of the optical informationrecording medium, thereby recording the first data. Therefore, datareproduction can be performed by changing the intensity of thediffracted light component.

Since the gray scale is expressed by the ratio of the line width to thegrating pitch of the diffraction gratings constituting the diffractiongrating cell, the distribution of the diffraction gratings is uniform,and the formability in embossing is good.

Since data recording is not related to the depth of the diffractiongrating, this optical information recording medium can be manufacturedby an apparatus, e.g., an electron beam lithography system capable ofbinary expression, which has a fine-processing capability. Control ofthe depth in the duplicate can be easily performed. This opticalinformation recording medium can be duplicated easily by, e.g.,embossing, thereby realizing mass production at a low cost.

According to the optical information recording medium of the secondaspect of the present invention, the second data is recorded byappropriately changing the grating pitch of the diffraction gratingsconstituting the diffraction grating cell based on the second originaldata used for manufacturing the optical information recording mediummain body. Thus, data reproduction by changing the diffraction angle ofthe diffracted light component can be performed.

Furthermore, according to the optical information recording medium ofthe second aspect of the present invention, the third data is recordedby appropriately changing the azimuth angle of the diffraction gratingsconstituting the diffraction grating cell based on the third originaldata used for manufacturing the optical information recording mediummain body. Thus, data reproduction by changing the exit direction of thediffracted light component can be performed.

According to the information reading method for the optical informationrecording medium of the second aspect of the present invention, wheninformation is to be read, one incident light beam is caused to beincident on the diffraction grating cell, and diffracted lightcomponents emerging from the diffraction grating cell are received bythe light-receiving elements, so that data is reproduced as a change inintensity of the diffracted light component, thereby reproducingmultivalue data.

According to the information reading method for the optical informationrecording medium of the second aspect of the present invention, wheninformation is to be read, one incident light beam is caused to beincident on the diffraction grating cell, and diffracted lightcomponents emerging from the diffraction grating cell are received bythe light-receiving elements, so that data is reproduced as a change indiffraction angle of the diffracted light component, thereby reproducinga plurality of data at once simultaneously.

According to the information reading method for the optical informationrecording medium of the second aspect of the present invention, wheninformation is to be read, one incident light beam is caused to beincident on the diffraction grating cell, and diffracted lightcomponents emerging from the diffraction grating cell are received bythe light-receiving elements, so that data is reproduced as a change inexit direction of the diffracted light component, thereby reproducing aplurality of data at once simultaneously.

According to the optical information recording medium of the thirdaspect of the present invention, a cell is divided into a plurality ofregions, in the same diffraction grating cell, the respective regionsare constituted by diffraction gratings having the same grating anglebut different grating pitches, and a grating pitch of the diffractiongratings constituting at least one of the respective regions isappropriately set based on original data used for manufacturing a mainbody of the optical information recording medium main body, therebyrecording data, so that reproduction of multivalue data by means of adiffraction angle of the diffracted light component of each region ofthe diffraction grating cell is performed.

According to the optical information recording medium of the thirdaspect of the present invention, the shapes and positions of therespective regions are appropriately set in units of cells based onoriginal data used for manufacturing the main body of the opticalinformation recording medium, thereby recording data, so that datareproduction by means of a change in spatial distribution of thediffracted light component of each region of the diffraction gratingcell is performed.

Furthermore, according to the optical information recording medium ofthe third aspect of the present invention, the azimuth angle of thediffraction gratings constituting the diffraction grating cell isappropriately changed based on the third original data used formanufacturing the main body of the optical information recording medium,thereby recording third data, so that data reproduction by means of achange in exit direction of the diffracted light component is performed.

From the foregoing, a plurality of different data can be recorded at aportion (constituted by a plurality of diffraction grating cellsdesigned for the same point on the chromaticity coordinates) which isseen only as the same color by observation with a naked eye. The presentinvention is not limited to recording in the same color, but anarbitrary image, e.g., a lithography pattern, can be formed in aplurality of colors.

According to the information reading method of the optical informationrecording medium of the third aspect of the present invention, wheninformation is to be read, one incident light beam is caused to beincident on a diffraction grating cell, and diffracted light componentsemerging from the diffraction grating cell are received by thelight-receiving elements, so that data is reproduced as a change indiffraction angle of the diffracted light component of each region ofthe diffraction grating cell, thereby reproducing a plurality of data atonce simultaneously.

According to the information reading method of the optical informationrecording medium of the third aspect of the present invention, wheninformation is to be read, one incident light beam is caused to beincident on the diffraction grating cell, and diffracted lightcomponents emerging from the diffraction grating cell are received bythe light-receiving elements, so that data is reproduced as the spatialdistribution of the diffracted light component in each region of thediffraction grating cell, thereby reproducing a plurality of data atonce simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 includes plan views each showing diffraction gratings as thefirst embodiment applied to an optical information recording mediumaccording to the first aspect of the present invention;

FIG. 2 is a schematic view showing the arrangement of an optical systemfor realizing an information reading method for an optical informationrecording medium according to the first embodiment;

FIG. 3 is a schematic view showing the arrangement of an optical systemfor realizing another information reading method for an opticalinformation recording medium according to the first embodiment;

FIG. 4 is a schematic view showing the arrangement of an optical systemfor realizing still another information reading method for an opticalinformation recording medium according to the first embodiment;

FIG. 5 includes schematic views showing the state of the informationreading method for the optical information recording medium according tothe first embodiment;

FIG. 6 includes schematic views showing the state of the informationreading method for the optical information recording medium according tothe first embodiment;

FIG. 7 includes schematic views showing the state of the informationreading method for the optical information recording medium according tothe first embodiment;

FIG. 8 is a plan view showing an optical information recording medium asthe second embodiment according to the second aspect of the presentinvention;

FIG. 9 includes plan views showing arrangements of one cell applied tothe optical information recording medium according to the second aspectof the present invention;

FIG. 10 is a graph showing an example of the relationship between theratio of the line width of diffraction gratings constituting the cell ofthe optical information recording medium as the second embodiment, tothe grating pitch, and a diffraction efficiency;

FIG. 11 is a sectional view showing the arrangement of rectangulardiffraction gratings constituting the cell of the optical informationrecording medium as the second embodiment;

FIG. 12 is a plan view showing the arrangement of the opticalinformation recording medium as the second embodiment applied to acard-like base material;

FIG. 13 is a schematic view showing the arrangement of an optical systemfor realizing an information reading method for the optical informationrecording medium as the second embodiment;

FIG. 14 is a schematic view showing the state of an information readingmethod for an optical information recording medium as the thirdembodiment according to the second aspect of the present invention;

FIG. 15 is a plan view showing an optical information recording mediumas the fourth embodiment according to the third aspect of the presentinvention;

FIG. 16 is a chromaticity diagram for explaining a method of setting thegrating pitch and the area ratio of the diffraction gratings of a cellapplied to the optical information recording medium as the fourthembodiment;

FIG. 17 is a view showing the state of diffraction in the opticalinformation recording medium as the fourth embodiment;

FIG. 18 is a plan view showing the arrangement of the opticalinformation recording medium as the fourth embodiment applied to acard-like base material;

FIG. 19 is a schematic view showing the arrangement of an optical systemfor realizing an information reading method for the optical informationrecording medium as the fourth embodiment;

FIG. 20 is a plan view showing the optical information recording mediumas the fifth embodiment according to the third aspect of the presentinvention;

FIG. 21 includes schematic views showing the arrangement of an opticalsystem for realizing an information reading medium for the opticalinformation recording medium as the fifth embodiment;

FIG. 22 is a plan view showing the optical information recording mediumas the sixth embodiment according to the third aspect of the presentinvention; and

FIG. 23 is a chromaticity diagram for explaining the method of settingthe grating pitch and an area ratio of the diffraction gratings of acell applied to the optical information recording medium as the sixthembodiment.

BEST MODE OF CARRYING OUT THE INVENTION

The gist of the first aspect of the present invention resides inrealization of an optical information recording medium which uses, asinformation recording elements, diffraction gratings consisting of aplurality of regions having at least one of different azimuth angles anddifferent grating pitches, and from which optical information can beread.

(First Embodiment)

FIGS. 1(a) to 1(d) are plan views respectively showing the arrangementsof diffraction gratings (to be merely referred to as a cell hereinafter)applied to an optical information recording medium according to thefirst aspect of the present invention.

More specifically, the cell shown in FIG. 1(a) consists of diffractiongratings in which curved gratings are aligned parallel to each other tohave a constant grating pitch. This cell is equally divided into aplurality of (in this embodiment, five in the horizontal direction)regions, and each divided region represents one binary data.

The cell shown in FIG. 1(b) consists of diffraction gratings in whichcurved gratings are aligned parallel to each other to have differentgrating pitches. This cell is equally divided into a plurality of (inthis embodiment, 3 in the horizontal direction ×3 in the verticaldirection =9) regions, and each divided region represents one binarydata.

The cell shown in FIG. 1(c) consists of diffraction gratings in whichconcentric circles are aligned at a constant gap. This cell is equallydivided into a plurality of (in this embodiment, 6 in thecircumferential direction) regions, and each divided region representsone binary data.

The cell shown in FIG. 1(d) consists of diffraction gratings in whichconcentric circles are aligned to have different gaps. This cell isequally divided into a plurality of (in this embodiment, 6 in thecircumferential direction) regions, and each divided region representsone binary data.

In this embodiment, at least one cell of FIGS. 1(a) to 1(d) is disposedon a planar substrate through a reflection layer, thus constituting areflection type optical information recording medium.

In the optical information recording medium having the abovearrangement, a cell comprising diffraction gratings is disposed on aplanar substrate, and the cell is divided into a plurality of regionshaving at least one of different azimuth angles and different gratingpitches, so that each divided region represents one binary data. Hence,a plurality of pieces of data can be recorded in one cell, therebyrecording information at a very high density.

To manufacture the optical information recording medium of thisembodiment, the following methods are available.

(a) Diffraction gratings are formed only on a region where data exists,by an apparatus, e.g., a electron beam lithography system which has afine-processing capability.

(b) Diffraction gratings are formed on the entire region by the method(a), and thereafter a light-shielding layer is formed on the surface ofa region where data does not exist, or the diffraction grating in aregion where data does not exist is destroyed.

In this case, since the diffraction grating drawn by the electron beamhas a comparatively simple shape, as shown in FIGS. 1(a) to 1(d), theamount of calculation can be small. Since the electron beam can beeasily controlled during drawing, the diffraction grating can bemanufactured comparatively easily. Since the optical informationrecording medium manufactured in this manner is of a surface relieftype, it can be manufactured in mass production at a low cost byemploying an embossing technique.

Furthermore, in the method (b), if a duplicate obtained by embossingfrom an original having the diffraction grating formed on its entiresurface is used and a light-shielding layer having coded individual datais formed on the surface of the duplicate later on, individualinformation can be input comparatively easily. Simultaneously, if aduplicate obtained by embossing is used, data is input bydestroying/non-destroying a corresponding region of a correspondingcell, and the optical information recording medium of this embodimentobtained in this manner is used as the embossing original. The opticalinformation recording medium can be manufactured in mass production at alow cost.

An information reading method for the optical information recordingmedium of this embodiment formed in the above manner will be described.

FIG. 2 is a schematic view showing the arrangement of an optical systemfor realizing an information reading method for the optical informationrecording medium according to this embodiment. FIG. 2 shows a casewherein a cell is used which is equally divided into five regions in thehorizontal direction, as shown in FIG. 1(a), such that each dividedregion represents one binary data.

Referring to FIG. 2, a substrate 1 is equally divided into five regionsin the horizontal direction, as in FIG. 1(a), and each divided regionrepresents one binary data. Beam-like incident light 3 can be caused tobe incident on this substrate 1 from a light source 2, e.g., a laserlight beam source. Light-receiving elements 4 corresponding in number tothe divided regions of the cell, i.e., five light-receiving elements 4are linearly disposed to correspond to the respective divided regions,thereby receiving light from the cell.

To read information from the optical information recording medium, thebeam-like incident light 3 is caused to be incident on the cell from thelight source 2. When the incident light 3 is incident on the cell,diffracted light components 5 emerge to all of the five light-receivingelements 4.

Accordingly, if binary data is expressed by providing or not providingthe light-shielding layer (or diffraction grating) in each of the fivedivided regions, the diffracted light components 5 emerge to onlylight-receiving elements 4 corresponding to divided regions where dataexist (data =1) in response to the incident light 3, as shown in FIG. 2,and data is reproduced. Reference numeral 6 denotes reflected light fromthe cell.

This means that the cell of this embodiment has an information recordingdensity which is five times that of one pit of a conventional opticalrecording disk. More specifically, whereas the conventional opticalrecording disk can record only one data in one pit, one data can berecorded in one divided region, and data corresponding in number to thedivided regions (five) can be recorded in one cell in the cell of thisembodiment.

when a plurality of cells are disposed on the planar substrate andoperations of reading five data instantaneously are sequentiallyperformed by rotating the substrate, for example, even if the rotatingspeed is the same as the conventional rotating speed, information can beread at a speed five times that the conventional information readingspeed.

FIG. 3 is a schematic view showing the arrangement of an optical systemfor realizing an information reading method for the optical informationrecording medium according to this embodiment. FIG. 3 shows a casewherein a cell is used which is equally divided into 3 in the horizontaldirection ×3 in the vertical direction =9 regions, as shown in FIG.1(b), such that each divided region represents one binary data.

Referring to FIG. 3, a substrate 11 is equally divided into 3 in thehorizontal direction ×3 in the vertical direction =9 regions, as in FIG.1(b), and each divided region represents one binary data. Beam-likeincident light 13 can be incident on this substrate 11 from a lightsource 12, e.g., a laser light beam source. Light-receiving elements 14corresponding in number to the divided regions of the cell, i.e., ninelight-receiving elements 14 are disposed in a matrix manner tocorrespond to the respective divided regions, thereby receiving lightfrom the cell.

To read information from the optical information recording medium, thebeam-like incident light 13 is caused to be incident on the cell fromthe light source 12. When the incident light 13 is incident on the cell,diffracted light components 15 emerge to all of the nine light-receivingelements 14.

Accordingly, if binary data is expressed by providing or not providingthe light-shielding layer (or diffraction grating) in each of the ninedivided regions, the diffracted light components 15 emerge to onlylight-receiving elements 14 corresponding to divided regions where dataexist (data =1) in response to the incident light 13, as shown in FIG.3, and data is reproduced. Reference numeral 16 denotes reflected lightfrom the cell.

This means that the cell of this embodiment has an information recordingdensity which is nine times that of one pit of a conventional opticalrecording disk. More specifically, whereas the conventional opticalrecording disk can record only one data in one pit, one data can berecorded in one divided region, and data corresponding in number to thedivided regions (nine) can be recorded in one cell in the cell of thisembodiment.

when a plurality of cells are disposed on the planar substrate andoperations of reading nine pieces of data at once are sequentiallyperformed by rotating the substrate, for example, even if the rotatingspeed is the same as the conventional rotating speed, information can beread at a speed nine times that the conventional information readingspeed.

FIG. 4 is a schematic view showing an arrangement of an optical systemfor realizing an information reading method for the optical informationrecording medium according to this embodiment. FIG. 4 shows a casewherein a cell is used which is equally divided into six regions in thecircumferential direction, as shown in FIG. 1(c) or 1(d), such that eachdivided region represents one binary data.

Referring to FIG. 4, a substrate 21 is equally divided into six regionsin the circumferential direction, as in FIG. 1(c) or 1(d), and eachdivided region represents one binary data. Beam-like incident light 23can be incident on this substrate 21 from a light source 22, e.g., alaser light beam source. Light-receiving elements 24 corresponding innumber to the divided regions of the cell, i.e., six light-receivingelements 24 are disposed in a circular manner to correspond to therespective divided regions, thereby receiving light from the cell.

To read information from the optical information recording medium, thebeam-like incident light 23 is caused to be incident on the cell fromthe light source 22. When the incident light 23 is incident on the cell,diffracted light components 25 emerge to all the six light-receivingelements

Accordingly, if binary data is expressed by providing or not providingthe light-shielding layer (or diffraction grating) in each of the sixdivided regions, the diffracted light components 25 emerge to onlylight-receiving elements 24 corresponding to divided regions where dataexist (data =1) in response to the incident light 23, as shown in FIG.4, and data is reproduced. Reference numeral 26 denotes reflected light(which propagates along the same optical axis as that of the incidentlight 23 in the opposite direction to the incident light 23) from thecell.

This means that the cell of this embodiment has an information recordingdensity which is six times that of one pit of a conventional opticalrecording disk. More specifically, whereas the conventional opticalrecording disk can record only one data in one pit, one data can berecorded in one divided region, and data corresponding in number to thedivided regions (six) can be recorded in one cell in the cell of thisembodiment.

When a plurality of cells are disposed on the planar substrate andoperations of reading six data instantaneously are sequentiallyperformed by rotating the substrate, for example, even if the rotatingspeed is the same as the conventional rotating speed, information can beread at a speed six times that the conventional information readingspeed.

FIGS. 5 to 7 are schematic views showing the states of the informationreading method for the optical information recording medium in FIGS. 3and 4 (in the case of FIGS. 1(c) and 1(d)). The same portions as inFIGS. 2 to 4 are denoted by the same reference numerals.

As described above, in the information reading method for the opticalinformation recording medium of this embodiment, one cell causesdiffracted light components to emerge in a plurality of directionssimultaneously upon reception of one incident light. Thus, a pluralityof data can be simultaneously reproduced by determining whether or notthe respective diffracted light components exist, so that informationreading at a very high speed can be realized.

The number of divided regions of the diffraction grating can beincreased by increasing the spot diameter of the beam-like incidentlight and the cell. Therefore, the number of exit directions of thediffracted light components can also be increased, so that a largernumber of pieces of information can be read at once.

Then, the spot diameter need not be decreased, unlike in theconventional case, and a lens system and the like for decreasing thespot diameter can be omitted or simplified.

When the cell shown in FIG. 1(b) or 1(b) is used, the cell can also havea function of focusing the diffracted light components. Then, errors inlight reception by the light-receiving elements can be furtherdecreased.

Furthermore, since the beam-like light is incident on the cell as theincident light, the diffracted light components emerging from the cellalso constitute a beam. Then, the light can be easily received by thelight-receiving elements, and a read error can be eliminated.

The gist of the second aspect of the present invention resides in thefollowing respects. Namely, when diffraction gratings are used as theinformation recording elements of an optical information recordingmedium, data is recorded by appropriately changing the ratio of the linewidth to the grating pitch of the diffraction gratings constituting thediffraction grating cell, so that the diffraction efficiency of thediffraction grating is controlled, that is, the intensity of thediffracted light component is changed during data reproduction, so thatdata can be read, thereby realizing an increase in density of datarecording.

Also, control of the diffraction efficiency is performed independentlyof recording information by using the grating pitch and the gratingazimuth angle, and control of the diffraction efficiency and informationrecording are combined as required to record independent data, therebyrealizing a further increase in density of data recording.

(Second Embodiment )

FIG. 8 is a plan view showing the arrangement of an reflection typeoptical information recording medium according to the present invention.

More specifically, as shown in FIG. 8, the optical information recordingmedium of this embodiment is constituted by disposing, on the surface ofa planar substrate 31, a plurality of cells 32, 33, and 34 comprisingsmall diffraction gratings through a reflecting layer (not shown).

The cell 32 records first data by appropriately changing the ratio ofthe line width to the grating pitch of the diffraction gratingsconstituting the cell 32 based on the first original data used formanufacturing this optical information recording medium.

The cell 33 records second data by appropriately changing the gratingpitch of the diffraction gratings constituting the diffraction gratingcell 33 based on the second original data used for manufacturing thisoptical information recording medium.

The cell 34 records third data by appropriately changing the azimuthangle of the diffraction gratings constituting the cell 34 based on thethird original data used for manufacturing this optical informationrecording medium.

In the cell 32, regarding the ratio of the line width to the gratingpitch of the diffraction grating, the intensity of the diffracted lightcomponent is coded based on the following equation: ##EQU2## where η isthe diffraction efficiency (a value of 0 to 1), r is the depth of thediffraction grating, l is the line width, d is the grating pitch, θ isthe azimuth angle of incidence of reproduced illumination light, and λis the wavelength of the reproduction illumination light.

Note that this equation is valid only for a surface relief typerectangular diffraction grating having a small depth.

FIG. 9 includes plan views showing arrangements of the diffractiongratings constituting the cell 32 of the above cells.

Referring to FIG. 9, when the line width of the diffraction gratingbecomes 1/2 the grating pitch, i.e., when line width: grating pitch=1:2, the diffraction efficiency becomes maximum, as shown in FIG. 10.When the difference between the line width and this value becomes large,the diffraction efficiency become lowered. FIG. 10 is obtained based onthe above equation.

Although recessed portions are expressed as lines in FIG. 9, projectingportions may be regarded as lines instead. FIG. 9 shows examples inwhich the diffraction gratings are formed by a three-dimensionalpattern. However, the diffraction grating may be formed in accordancewith any method, i.e., a method of changing the light transmittance,reflectance, or the phase (to form the diffraction grating with athree-dimensional pattern correspond to change the phase between therecessed portions and the projecting portions).

An example is a method of forming the diffraction grating by changingthe light transmittance or reflectance includes a method of expressingthe diffraction grating by changing the density (to express portionscorresponding to the recessed or projecting portions in FIG. 9 in black(light absorption or light shielding) and white (reflection ortransmittance)).

Another example of forming the diffraction grating by changing the phaseincludes a method of forming the grating with layers of two media havingdifferent refractive indices (to form portions corresponding to therecessed and projecting portions in FIG. 9 with different media).

FIG. 11 is a sectional view showing the arrangement of a rectangulardiffraction grating formed with a three-dimensional surface pattern.

As shown in FIG. 11, when the optical information recording medium ofthis embodiment is formed with the three-dimensional pattern, thedepthwise directions can be sufficiently expressed by binary expression.Accordingly, this optical information recording medium can bemanufactured also by using a binary device, e.g., an electron beamlithography system, to have a good formability in accordance with simpleduplicating process without requiring depth control and the like.

FIG. 12 is a plan view showing an example of a case wherein the opticalinformation recording medium of this embodiment is applied to acard-like base material.

As shown in FIG. 12, since the thickness of the optical informationrecording medium of this embodiment can be greatly decreased, even when,e.g., this optical information recording medium is adhered to acard-like base material, no problem arises concerning the thickness.

In the optical information recording medium of this embodiment havingthe above arrangement, the ratio of the line width to the grating pitchof the diffraction gratings constituting the cell 32 is approximatelychanged based on the first original data used for manufacturing the mainbody of the optical information recording medium, thereby recording thefirst data. Therefore, data reproduction can be performed by changingthe intensity of the diffracted light component, so that information canbe recorded at a very high density.

Since the multivalue is expressed by the ratio of the line width to thegrating pitch of the diffraction gratings constituting the cell 32, thedistribution of the diffraction grating becomes uniform, and theformability in embossing becomes good.

Since data recording is not related to the depth of the diffractiongrating, this optical information recording medium can be manufacturedby an apparatus, e.g., an electron beam lithography system capable ofbinary expression, which has a fine-processing capability. Control ofthe depth in the duplicate can be easily performed. Since the opticalinformation recording medium is of the surface relief type, it can beduplicated easily by, e.g., embossing, thereby realizing mass productionat a low cost.

More specifically, since the diffraction grating is formed to bespatially uniform, it has a good formability in the duplicating process.Since it suffices if the diffraction grating has a uniform depth,conditions for duplication become moderate, thereby facilitatingduplication.

From the foregoing, a multivalue expression of a stable(high-reliability) optical information recording medium can be realizedwhile facilitating duplication.

In addition to the above characteristics concerning the diffracted lightintensity, in the optical information recording medium of thisembodiment, the second data is recorded by appropriately changing thegrating pitch of the diffraction gratings constituting the cell 33 basedon the second original data used for manufacturing the opticalinformation recording medium main body. Thus, data reproduction bychanging the diffraction angle of the diffracted light component can beperformed, thereby enabling higher-density information recording.

In addition to the above characteristics concerning the diffracted lightintensity, in the optical information recording medium of thisembodiment, the third data is recorded by appropriately changing theazimuth angle of the diffraction gratings constituting the cell 34 basedon the third original data used for manufacturing the opticalinformation recording medium main body. Thus, data reproduction bychanging the exit direction of the diffracted light component can beperformed, thereby enabling higher-density information recording.

An information reading method for the optical information recordingmedium of this embodiment having the above arrangement will bedescribed.

FIG. 13 is a schematic view showing the arrangement of an optical systemfor realizing an information reading method for the optical informationrecording medium (reflection type) of this embodiment. Only one cell onthe substrate 1 will be considered.

Referring to FIG. 13, beam-like incident light 37 can be verticallyincident on a substrate 31, on which a cell 35 recording data is formed,from a light source 36, e.g., a laser light beam source. A plurality oflight-receiving elements 38 are circularly disposed, as shown in FIG.13, thereby receiving diffracted light components 39 and 310 from thecell 35.

When information on the optical information recording medium is to beread, the beam-like incident light 37 from the light source 36 is causedto be vertically incident on the cell 35. When the incident light 37 isvertically incident on the cell 35, diffracted light components of ±1storder emerge with a symmetrical positional relationship.

A case will be considered wherein only +1 st-order diffracted lightcomponent 39 is detected by a light-receiving element 38 indicated as asolid element in FIG. 13 and no light is detected by otherlight-receiving elements 38. In this case, the grating interval and theazimuth angle of grating of the diffraction grating of a cell inquestion can be obtained from the position of the light-receivingelement 38 indicated as the solid element. The ratio of the line widthto the grating pitch of the diffraction grating of the cell can beobtained from the light intensity detected by the light-receivingelement 38.

More specifically, when the grating pitch of the diffraction grating issmaller than that of the diffraction grating shown in FIG. 13, thediffracted light component is detected by a light-receiving element 38at an outer side which is located in the same circumferential directionin accordance with the following equation.

The diffracted light component obtained by the diffraction grating isexpressed by the following equation:

    mλ=d(sin α+sin β)

where λ is the wavelength of the illumination light (incident light), dis the grating pitch, α is the angle of incidence of the illuminationlight, and β is the exit angle of mth-order diffracted light component.Usually, a diffracted light component having an m=1 st order, i.e., +1st-order diffracted light component is considered.

When the azimuth angle of the diffraction grating is changed, thediffracted light component is detected by a light-receiving element 38having the same distance in the direction of diameter but differentposition on the circumferential direction accordingly.

When the ratio of the line width to the grating pitch of the diffractiongrating is changed, the light intensity of the diffracted lightcomponent detected by the light-receiving element 38 is changedaccordingly.

Therefore, in the optical information recording medium of thisembodiment, first to third three different types of independent piecesof information can be recorded only by a cell on which reproductionillumination light (described as incident light 7 in FIG. 13) isincident. In addition, since each of these three types of informationcan record binary data or data having three or more values, high-densityrecording can be performed.

Furthermore, when the incident light 37 is scanned or the substrate 31is moved, large-capacity information can be read at a speed a pluralityof times the conventional speed even if the scanning speed or rotatingspeed is the same as the conventional one.

(Third Embodiment)

FIG. 14 is a schematic view showing the state of an information readingmethod for an optical information recording medium on which data isrecorded by changing only the line width and the grating pitch. The sameportions as in FIG. 13 are denoted by the same reference numerals. Notethat FIG. 14 shows a transmission type optical information recordingmedium.

Referring to FIG. 14, upon incidence of incident light (parallel light)37 having a certain wavelength, cells having different grating pitchesemerge diffracted light components in different directions, as indiffracted light components 311 and 312. Since ratios of the line widthsto the grating pitches of the diffraction gratings are different, thelight intensities of the diffracted light components 311 and 312 arealso different. The diffraction angles and light intensities of thediffracted light components 311 and 312 can be obtained by detecting thediffracted light components 311 and 312 by light-receiving elements 38,and original information can be reproduced from the obtained diffractionangles and light intensities.

As described above, in the information reading method for the opticalinformation recording medium of this embodiment, one cell causesdiffracted light components to emerge in a plurality of directionssimultaneously upon reception of one incident light 37. Since aplurality of data can be simultaneously reproduced, information readingat a very high speed can be realized.

The number of exit directions of the diffracted light components can beincreased by increasing the spot diameter of the incident light 37 andthe number of cells, so that a larger number of pieces of informationcan be read simultaneously.

Then, the spot diameter need not be decreased, unlike in theconventional case, and a lens system and the like for decreasing thespot diameter can be omitted or simplified.

Furthermore, when a plurality of light beams corresponding to therespective cells are incident on the cells as the incident light 37, thediffracted light component emerging from each cell is also a beam. Then,the light can be easily received by the light-receiving elements, and aread error can be eliminated.

In the above description, note that the azimuth angle of the diffractiongrating indicates the angle through which the diffraction grating ispivoted about the normal to the surface of the substrate as the pivotaxis, that the diffraction angle of the diffracted light componentindicates the angle at which the diffracted light component emerges withrespect to the normal to the surface of the substrate, and that the exitdirection of the diffracted light component indicates the pivotingdirection about the normal to the surface of the substrate as the pivotaxis.

The gist of the third aspect of the present invention resides in thefollowing respects. Namely, when diffraction gratings are used as theinformation recording elements of an optical information recordingmedium, the diffraction grating cell is divided into a plurality ofregions, in the same diffraction grating cell, the respective regionsare constituted by diffraction gratings having the same azimuth anglebut different grating pitches,

(a) the grating pitch of diffraction gratings constituting at least oneof the respective regions is appropriately set based on the originaldata used for manufacturing the optical information recording mediummain body, thereby recording data, or

(b) the shapes and positions of the respective regions are appropriatelyset in units of diffraction grating cells based on the original dataused for manufacturing the optical information recording medium mainbody, thereby recording data, or

(c) the grating pitch of the diffraction gratings constituting at leastone of the respective regions is appropriately set based on the firstoriginal data used for manufacturing the optical information recordingmedium main body, thereby recording the first data, and the shapes andpositions of the respective regions are appropriately set in units ofthe diffraction grating cells based on the second original data used formanufacturing the optical information recording medium main body,thereby recording the second data, and

thus data is recorded by using the area ratios of the respective regionsor a plurality of types of grating pitches, that is, data read isenabled by realizing change in spatial distribution and in diffractionangles of the diffracted light components in the respective regionsduring data reproduction, thereby realizing high-density data recording.

The gist of the third aspect of the present invention also resides inthat this data recording is performed independently of informationrecording by using the azimuth angle of the diffraction grating, andthis data recording and information recording by using the azimuth angleof the diffraction grating are combined as required to recordindependent data, thereby realizing a further increase in density ofdata recording.

(Fourth Embodiment)

FIG. 15 is a plan view showing the arrangement of an optical informationrecording medium according to this embodiment.

More specifically, as shown in FIG. 15, the optical informationrecording medium of this embodiment is formed by disposing, on thesurface of a planar substrate 41, a plurality of cells 42 comprisingsmall diffraction gratings through a reflecting layer (not shown).

As shown in FIG. 15, each cell 42 is divided into a plurality of (two inthis embodiment) regions, in the same cell 42, the respective regionsare constituted by diffraction gratings having the same azimuth anglebut different grating pitches, and the grating pitch of the diffractiongratings constituting at least one of the respective regions isappropriately set based on the original data used for manufacturing theoptical information recording medium main body, thereby recording data.

More specifically, the grating pitch and the area ratio of thediffraction gratings of each region are determined based on the originaldata used for manufacturing the optical information recording medium soas to change the diffraction angle and the intensity of the diffractedlight component of the diffraction gratings of each region. In thiscase, the grating pitch and the area may be determined while consideringthe conditions for visual observation as well.

More specifically, when, e.g., the respective cells are to be observedin the same color, as shown in FIG. 16, the grating pitch of thediffraction grating and the area of the region are set such that theratio of the wavelength to the intensity of a diffracted light componentemerging from each region of the same cell corresponds to the color ofone point on a chromaticity diagram (refer to CIE, auxiliary standardobserver, 1964) for each cell, that is, the grating pitches of tworegions of each cell 42 are formed by the pair of the wavelengths atpoints on the two ends of a line segment extending through a certainpoint on the chromaticity diagram.

The diffraction grating used in the present invention may be formed inaccordance with any method, i.e., a method of changing the lighttransmittance, reflectance, or phase.

An example of forming the diffraction grating by changing the lighttransmittance or reflectance includes a method of expressing thediffraction grating by changing the density.

An example of forming the diffraction grating by changing the phaseincludes a method of forming the diffraction grating with athree-dimensional pattern, and a method of forming the diffractiongrating with layers of two media having different refractive indices (toform portions corresponding to the recessed and projecting portions withdifferent media).

FIG. 11 is a sectional view showing the arrangement of a rectangulardiffraction grating formed with a three-dimensional surface pattern.

As shown in FIG. 11, when the optical information recording medium ofthis embodiment is formed with the three-dimensional pattern, thedepthwise directions can be sufficiently expressed by binary expression.Accordingly, this optical information recording medium can bemanufactured also by using a binary device, e.g., an electron beamlithography system, to have a good formability in accordance with simpleduplicating process without requiring depth control and the like.

Diffraction gratings may also be manufactured by recording aninterference fringe on a photosensitive material for each region byutilizing coherence of laser light beam.

As shown in FIG. 17, the diffracted light component obtained by thediffraction grating is expressed by the following equation:

    mλ=d(sinα+sinβ)

where λ is the wavelength of the illumination light (incident light), dis the grating pitch, α is the angle of incidence of the illuminationlight, and β is the exit angle of mth-order diffracted light component.Usually, a diffracted light component having an m=+1 st order, i.e.,1st-order diffracted light component is considered.

FIG. 18 is a plan view showing an example of a case wherein the opticalinformation recording medium of this embodiment is applied to acard-like base material.

As shown in FIG. 18, since the thickness of the optical informationrecording medium of this embodiment can be greatly decreased, even when,e.g., this optical information recording medium is adhered to acard-like base material, no problem arises concerning the thickness.

In the optical information recording medium of this embodiment havingthe above arrangement, each cell is divided into two regions, in thesame cell 42, the respective regions are constituted by diffractiongratings having the same azimuth angle but different grating pitches,and the grating pitch of the diffraction gratings constituting at leastone of the respective regions is appropriately set based on the originaldata used for manufacturing the optical information recording mediummain body, thereby recording data. Since data reproduction can beperformed by changing the spatial distribution of the diffracted lightcomponents of the respective regions of the cell 42, information can berecorded at a very high density.

The color obtained by observation with a naked eye depends on thegrating pitches and the area ratios of the diffraction gratings of therespective regions of the cells 42. When data is recorded in one cell 2by means of the grating pitches of one region, if the grating pitches ofthe remaining regions and the area ratio are appropriately set, the samecolor can be observed.

Thus, a plurality of different data can be recorded at a portion(constituted by a plurality of cells 42 designed for the same point onthe chromaticity coordinates) which is seen only as the same color byobservation with a naked eye.

More specifically, since the grating pitches of two regions in each cell42 are constituted by a pair of wavelengths at points on the two ends ofa line segment extending through a certain point on the chromaticitydiagram, when white light is caused to be incident on this opticalinformation recording medium and observation with a naked eye isperformed, all the cells 42 look shining in the same color. However, iflight having a single wave length, e.g., a laser beam is caused toincident on this optical information recording medium and itsdiffraction angle is obtained, different data can be reproduced in unitsof cells 42. This is because light having wavelengths corresponding tothe respective grating pitches emerges at a certain angle when lightincluding all the wavelengths, i.e., white light is considered, andbecause light emerges at angles corresponding to the respective gratingpitches when light having a single wavelength is considered (refer tothe above equation). Hence, recorded data cannot be known with a nakedeye.

In addition, data recording is not limited to recording in the samecolor, but it is also possible to form an arbitrary image, e.g., apattern, by using a plurality of colors.

From the foregoing, the security effect can be improved by concealinginformation under the ordinary conditions.

Furthermore, since data recording is not related to the depth of thediffraction grating, this optical information recording medium can bemanufactured by an apparatus, e.g., an electron beam lithography systemcapable of binary expression, which has a fine-processing capability.Control of the depth in the duplicate can be easily performed. Theoptical information recording medium can be duplicated easily by, e.g.,embossing, thereby realizing mass production at a low cost.

An information reading method for the optical information recordingmedium of this embodiment having the above arrangement will bedescribed.

FIG. 19 is a schematic view showing the arrangement of an optical systemfor realizing an information reading method for the optical informationrecording medium of this embodiment. Only one cell on the substrate 41will be considered.

Referring to FIG. 19, beam-like incident light 47 can be verticallyincident on a substrate 41, on which a cell 45 recording data isdisposed, from a light source 46, e.g., a laser light beam source. Aplurality of light-receiving elements 48 are circumferentially disposed,as shown in FIG. 19, thereby receiving diffracted light components 49and 410 from the cell 45.

when information on the optical information recording medium is to beread, the beam-like incident light 47 from the light source 46 is causedto be vertically incident on the cell 45. When the incident light 47 isvertically incident on the cell 45, diffracted light components of the±1st order emerge with a symmetrical positional relationship.

A case will be considered wherein only +1 st-order diffracted lightcomponent 49 is detected by a light-receiving element 48 indicated as asolid element in FIG. 19 and no light is detected by otherlight-receiving elements 48. In this case, the grating interval and theazimuth angle of grating of the diffraction grating of a cell inquestion can be obtained from the position of the light-receivingelement 48 indicated as the solid element.

More specifically, when the grating pitch of the diffraction grating issmaller than that of the diffraction grating shown in FIG. 19, thediffracted light component is detected by a light-receiving element 48at an outer side which is located in the same circumferential directionin accordance with the above equation.

When the azimuth angle of the diffraction grating is changed, thediffracted light component is detected by a light-receiving element 48at a different position on the circumferential direction accordingly.

Therefore, in the optical information recording medium of thisembodiment, a plurality of pieces of independent information can berecorded only by a cell on which reproducing illumination light(described as incident light 47 in FIG. 19) is incident. In addition,since each of these three types of information can record binary data ordata having three or more values, high-density recording can beperformed.

Furthermore, when the incident light 47 is scanned or the substrate 41is moved, large-capacity information can be read at a speed a pluralityof times the conventional speed even if the scanning speed or rotatingspeed is the same as the conventional one.

Since the beam-like light is caused to be incident on the cell as theincident light 47, the diffracted light components emerging from thecell also constitute a beam. Then, not only light reception by thelight-receiving elements 48 becomes easy, but also a read error can beeliminated.

(Fifth Embodiment)

FIG. 20 is a plan view showing the arrangement of an optical informationrecording medium according to this embodiment.

More specifically, as shown in FIG. 20, the optical informationrecording medium of this embodiment is formed by disposing, on thesurface of a planar substrate 411, a plurality of cells 412 comprisingsmall diffraction gratings through a reflecting layer (not shown).

As shown in FIG. 20, each cell 412 is divided into a plurality of (two,three, and four in this embodiment) regions, in the same cell 412, therespective regions are constituted by diffraction gratings having thesame azimuth angle but different grating pitches, and the shapes andpositions of the respective regions are appropriately set in units ofdiffraction grating cells based on the original data used formanufacturing the optical information recording medium main body,thereby recording data.

More specifically, the grating pitch and the area ratio of thediffraction gratings of each region are determined based on the originaldata used for manufacturing the optical information recording medium soas to change the diffraction angle and the intensity of the diffractedlight component of the diffraction gratings of each region. In thiscase, the grating pitch and the area may be determined while consideringthe conditions for visual observation as well.

More specifically, when, e.g., the respective cells are to be observedin the same color, the grating interval of the diffraction grating andthe area of the region are set such that the ratio of the wavelength tothe intensity of a diffracted light component emerging from each regionof the same cell corresponds to the color of one point on a chromaticitydiagram for each cell, that is, the grating pitches of two regions ofeach cell 412 are formed by the pair of the wave-lengths at points onthe two ends of a line segment extending through a certain point on thechromaticity diagram.

This embodiment shows a case wherein all the cells 412 consist ofdiffraction gratings having common two types of grating pitches. Thediffraction grating used in this embodiment may be formed in accordancewith any method, i.e., a method of changing the light transmittance,reflectance, or phase.

An example of forming the diffraction grating by changing the lighttransmittance or reflectance includes a method of expressing thediffraction grating by changing the density.

An example of forming the diffraction grating by changing the phaseincludes a method of forming the diffraction grating with athree-dimensional pattern, and a method of forming the diffractiongrating with layers of two media having different refractive indices (toform portions corresponding to the recessed and projecting portions withdifferent media).

In the optical information recording medium of this embodiment havingthe above arrangement, each cell 412 is divided into two regions, in thesame cell 412, the respective regions are constituted by diffractiongratings having the same azimuth angle but different grating pitches,and the shapes and positions of the respective regions are appropriatelyset in units of diffraction gratings based on the original data used formanufacturing the optical information recording medium main body,thereby recording data. Since data reproduction can be performed bychanging the spatial distribution of the diffracted light components ofthe respective regions of the cell 412, information can be recorded at avery high density.

The color obtained by observation with a naked eye depends on thegrating pitches and the area ratios of the diffraction gratings of therespective regions of the cells 412. If the area ratios of two types ofdiffraction gratings of the respective cells 412 are the same, thesecells 412 can be observed as cells having the same color.

Thus, a plurality of different data can be recorded at a portion whichis seen only as the same color by observation with a naked eye.

More specifically, since the respective regions of the respective cells412 have two common types of diffraction gaps and the same area ratio,they correspond to a certain point on the chromaticity diagram. Whenwhite light is caused to be incident on this optical informationrecording medium and observation with a naked eye is performed, all thecells 412 look shining in the same color. However, if light an azimuthangle, e.g., a laser beam is caused to incident on this opticalinformation recording medium and the spatial distribution of thediffracted light components is obtained, different data can bereproduced in units of cells 412. Hence, recorded data cannot be knownwith a naked eye.

In addition, data recording is not limited to recording in the samecolor, but it is also possible to form an arbitrary image, e.g., apattern, by using a plurality of colors.

From the foregoing, the security effect can be improved by concealinginformation under the ordinary conditions.

Furthermore, since data recording is not related to the depth of thediffraction grating, this optical information recording medium can bemanufactured by an apparatus, e.g., an electron beam lithography systemcapable of binary expression, which has a fine-processing capability.Control of the depth in the duplicate can be easily performed. Theoptical information recording medium can be duplicated easily by, e.g.,embossing, thereby realizing mass production at a low cost.

An information reading method for the optical information recordingmedium of this embodiment having the above arrangement will bedescribed.

FIG. 21(a) is a schematic view showing the arrangement of an opticalsystem for realizing an information reading method for the opticalinformation recording medium of this embodiment. Only one cell on thesubstrate 411 will be considered.

Referring to FIG. 21(a), parallel incident light 417 can be caused to bevertically incident on the substrate 411, on which a cell 415 recordingdata is disposed, from a light source 416, e.g., a laser light beamsource. A plurality of (two in this embodiment) photodetectors 418A and418B are disposed, as shown in FIG. 21(a), thereby receiving diffractedlight components 419A and 419B from the cell 15.

when information on the optical information recording medium is to beread, the incident light 417 from the light source 416 is caused to bevertically incident on the cell 415. When the incident light 417 isvertically incident on the cell 415, two diffracted light componentshaving different angles of diffraction emerge.

More specifically, a difference in grating pitch leads to a differencein diffraction angle, and patterns expressed by diffraction gratingshaving individual grating pitches are detected by the two photodetectors418A and 418B, as shown in FIG. 21(b) (in FIG. 21(b), diffracted lightcomponents of -1 st order and the like are omitted). The photodetectors418A and 418B are illustrated as those formed by aligninglight-receiving elements, as in, e.g., CCD array.

In this case, since these patterns are inverted patterns to each other,it suffices in practice if either a photodetector 418A or 418B isprovided. Then, the mechanical structure for information read accessbecomes simple, and easy information reading is enabled. From thesepoints, the optical information recording medium of this embodiment canbe treated in the same manner as a bar code or the like which isexpressed in an ordinary printing ink.

Accordingly, in the optical information recording medium of thisembodiment, a plurality of pieces of independent information can berecorded only at a cell on which reproduction illumination light(described as the incident light 417 in FIG. 21) is incident. Inaddition, since each of these plurality of types of information canrecord binary data or data having three or more values, high-densityrecording can be performed.

When the incident light 417 is scanned or the four substrates 11 aremoved, large-capacity information can be read at a speed a plurality oftimes the conventional speed even if the scanning speed or rotatingspeed is the same as the conventional one.

when the patterns of the diffracted light components 419A and 419Brespectively detected by the two photodetectors 418A and 418B arecompared, whether or not the read information is valid data can bechecked.

As described above, in the information reading method for the opticalinformation recording medium of this embodiment, since one cell causesdiffracted light components to emerge in a plurality of directionssimultaneously upon reception of one incident light beam 47, a pluralityof data can be reproduced simultaneously, thereby realizing informationreading at a very high speed.

When the spot diameter of the incident light 417 and the cell areincreased, a larger number of pieces of information can be read at once.

Then, the spot diameter need not be decreased, unlike in theconventional case, and a lens system and the like for decreasing thespot diameter can be omitted or simplified.

Since parallel light is caused to be incident on the cell as theincident light 417, the diffracted light components emerging from thecell also become parallel light. Then, not only light reception by thephoto-detectors 418A and 418B becomes easy, but also a read error can beeliminated.

In the above description, note that the azimuth angle of the diffractiongrating indicates the angle through which the diffraction grating ispivoted about the normal to the surface of the substrate as the pivotaxis, that the diffraction angle of the diffracted light componentindicates the angle at which the diffracted light component is emittedwith respect to the normal to the surface of the substrate, and that theexit direction of the diffracted light component indicates the pivotingdirection about the normal to the surface of the substrate as the pivotaxis.

(Sixth Embodiment)

The above fifth embodiment and the sixth embodiment exemplify caseswherein data is recorded by using only cells in which, in the same cell,the respective regions are constituted by diffraction gratings havingthe same azimuth angle and different grating pitches. However, thepresent invention is not limited to this. When another data is recordedby changing the grating azimuth angles of the diffraction gratings ofthe respective regions based on another original data used formanufacturing an optical information recording medium, higher-densityinformation recording is enabled.

FIG. 22 is a plan view showing the arrangement of a reflection typeoptical information recording medium according to this embodiment ofthis type.

More specifically, referring to FIG. 22, the optical informationrecording medium of this embodiment is constituted by disposing, on thesurface of a planar substrate 421, a plurality of cells 422 comprisingsmall diffraction gratings through a reflecting layer (not shown).

The diffraction gratings constituting the respective cells 422 are asshown in FIG. 22, and each cell 422 consists of diffraction gratingshaving two types of grating pitches.

In the cells 422 constituting the upper horizontal bar of a letter "T"in FIG. 22, the two types of grating pitches are common, and only thearea ratios are different. For example, if the two types of gratingpitches are set such that the wavelengths are 500 nm and 600 nm inobservation, all the points on the line segments of the chromaticitydiagram shown in FIG. 23 can be expressed by the area ratio of the tworegions.

At this time, the ratio of p to q in FIG. 23 is equal to the area ratiosof the respective regions. Accordingly, the cells 422 forming the upperhorizontal bar of the letter "T" in FIG. 23 are observed in a colorlocated at a position, on the line segment defined by the two gratingpitches, of the p-q ratio equal to the area ratio.

In the cells 422 forming the vertical bar of the letter "T" shown inFIG. 23, the two types of grating pitches are common, and only thegrating azimuth angles and the shapes of the respective regions aredifferent.

when these facts are utilized, in the optical information recordingmedium of this embodiment, machine-reading information which cannot berecognized by visual observation can be recorded in a cell group whichis seen in an arbitrary color of a range within a solid line on thechromaticity diagram in observation with a naked eye. Inversely, animage, e.g., a graphic pattern, which can be visually identified may beobserved completely independently of the machine-reading information.

From the foregoing, the security effect can be further improved byconcealing information under the ordinary conditions and/or by matchingthe visual-observation information and the machine-reading information.

In this embodiment, the number of grating pitches of the diffractiongratings of the cells and the number of divided regions are not limitedto two in the same manner as in the embodiments described above.

The present invention is not limited to this embodiment, but cansimilarly be practiced in the following manner as well.

(a) In FIGS. 1(a) to 1(d) of the first embodiment, the number of dividedregions may be a number other than the described number as far as it isplural. The dividing direction may be either vertical or horizontalespecially in FIGS. 1(a) and 1(b).

(b) In FIGS. 1(c) and 1(d) of the first embodiment, the diffractiongrating is not limited to a true circle but can be an ellipse.

(c) In the first embodiment, data 1 represents a case whereindiffraction gratings are present and a diffracted light component isincident on a light-receiving element. Inversely, however, data 0 mayrepresent a case wherein diffraction gratings are present and adiffracted light component is incident on a light-receiving element, anddata 1 may represent a case wherein a diffracted light component is notincident on a light-receiving element.

(d) FIGS. 1(a) and 1(b) of the first embodiment exemplify cases whereina diffraction grating cell in which curved gratings are aligned parallelto each other to have constant or different grating pitches is used asthe diffraction grating cell. However, the present invention is notlimited to this. Even when a diffraction grating cell in which curvedgratings, i.e., linear gratings having continuously changing gradientsare aligned parallel to each other to have constant or different gratingpitches is used, the same effect as that described above can berealized.

(e) The first embodiment exemplifies a case wherein a reflection typediffraction grating cell is used as the diffraction grating cell.However, the present invention is not limited to this, and atransmission type diffraction grating cell may also be employed as thediffraction grating cell. In this case, since a reflecting layer neednot be provided when disposing the diffraction grating cell on thesubstrate, the manufacturing step of the optical information recordingmedium can be simplified accordingly.

(f) The first embodiment exemplifies a case wherein beam-like light iscaused to be incident as incident light. However, the present inventionis not limited to this.

(g) FIG. 13 of the second embodiment exemplifies a case wherein areflection type cell is used as the cell, and FIG. 14 of the thirdembodiment exemplifies a case wherein a transmission type cell is usedas the cell. However, the present invention is not limited to these. Itis possible to use a transmission type cell as the cell in FIG. 13 ofthe second embodiment, and a reflection type cell as the cell in FIG. 14of the third embodiment.

When a transmission type cell is used as the cell, a reflecting layerneed not be provided when the diffraction grating cell is formed on thesubstrate. Therefore, the manufacturing step of the optical informationrecording medium can be simplified accordingly.

(h) The second and third embodiments exemplify cases wherein an opticalinformation recording medium is formed by forming a plurality of cellscomprising small diffraction gratings on the surface of a planarsubstrate. However, the present invention is not limited to this. Thepresent invention can similarly be applied to a case wherein an opticalinformation recording medium is formed by forming at least one cell onthe surface of a planar substrate.

(i) The second and third embodiments exemplify cases wherein an opticalinformation recording medium records the first to third, i.e., threetypes of data. However, the present invention is not limited to this. Itsuffices if an optical information recording medium records at least thefirst data.

(j) FIG. 13 of the second embodiment exemplifies a case whereinbeam-like light is caused to be incident as the incident light, and FIG.14 of the third embodiment exemplifies a case wherein parallel light iscaused to be incident as the incident light. However, the presentinvention is not limited to these. Parallel light may be caused to beincident as the incident light in FIG. 13 of the second embodiment, andbeam-like light may be caused to be incident as the incident light inFIG. 14 of the third embodiment.

(k) The second and third embodiments exemplify cases wherein the firstto third, i.e., three types of data are recorded by different cells.However, the present invention is not limited to this, and these datamay be recorded simultaneously by one cell.

(l) The second and third embodiments exemplify cases wherein a pluralityof light-receiving elements are used. However, the present invention isnot limited to this. When only the intensity of the diffracted lightcomponent is to be read, it suffices if at least one light-receivingelement is provided.

(m) The fourth to sixth embodiments exemplify cases wherein a reflectiontype cell is used as the cell. However, the present invention is notlimited, and a transmission type cell may be used as the cell. In thiscase, since a reflecting layer need not be provided when forming thediffraction grating cell on the substrate, the manufacturing step of theoptical information recording medium can be simplified accordingly.

(n) The fourth to sixth embodiments exemplify cases wherein an opticalinformation recording medium is formed by forming a plurality of cellscomprising small diffraction gratings on the surface of a planarsubstrate. However, the present invention is not limited to this. Thepresent invention can similarly be applied when an optical informationrecording medium is to be formed by forming at least one cell on thesurface of a planar substrate.

(o) FIG. 15 of the fourth embodiment exemplifies a case wherein the cellis divided into two regions. However, the present invention is notlimited to this, and three or more wavelengths may be selected toindicate a point on the chromaticity diagram. In this case, aninformation amount per cell can be increased.

(p) FIG. 20 of the fifth embodiment exemplifies a case wherein each ofall the cells consists of diffraction gratings having two differentgrating pitches. However, the present invention is not limited to this.The present invention can similarly be applied to a case wherein each ofall the cells consists of diffraction gratings having three or moredifferent grating pitches.

(q) The fourth and fifth embodiments exemplify cases wherein beam-likeor parallel light is caused to be incident as the incident light.However, the present invention is not limited to this.

(r) The fourth to sixth embodiments exemplify cases wherein data isrecorded and read in accordance with at least one grating pitch of therespective regions of a cell or in accordance with the shapes andpositions of the respective regions in a cell. However, the presentinvention is not limited to this, and the above data recording/readingmay be performed simultaneously.

We claim:
 1. An optical information recording medium characterized inthatat least one cell comprising diffraction gratings is disposed on aplanar substrate, and said cell is divided along two dimensions into n(n is an integer of not less than 2) regions such that each dividedregion represents one binary data.
 2. An optical information recordingmedium according to claim (1), characterized in that a cell comprisingdiffraction gratings having at least either different azimuth angles ordifferent grating pitches and formed in said divided regions is used assaid cell.
 3. An optical information recording medium according to claim(1), characterized in that a cell comprising diffraction gratings whichare obtained by aligning curved gratings parallel to each other to haveconstant grating pitches is used as said cell.
 4. An optical informationrecording medium according to claim (1), characterized in that a cellcomprising diffraction gratings which are obtained by aligning curvedgratings parallel to each other to have different grating pitches isused as said cell.
 5. An optical information recording medium accordingto claim (1), characterized in that a cell comprising diffractiongratings which are obtained by aligning concentric circles at apredetermined gap is used as said cell, and said cell is divided into nregions by lines extending through the center of the concentric circlessuch that each divided region represents one binary data.
 6. An opticalinformation recording medium according to claim (1), characterized inthat a cell comprising diffraction gratings which are obtained byaligning concentric circles at different gaps is used as said cell, andsaid cell is divided into n regions by lines extending through thecenter of the concentric circles such that each divided regionrepresents one binary data.
 7. An optical information recording mediumaccording to claim 1, wherein either a reflection type cell or atransmission type cell is used as said cell.
 8. A method of readinginformation on an optical information recording medium, comprising thesteps of:disposing at least one cell comprising diffraction gratings ona planar substrate; dividing said at least one cell into n regions suchthat each of said n regions represents one binary data, n being aninteger of not less than 2; disposing light-receiving elementscorresponding in number to said number n of divided regions of saidcell, said light receiving elements being disposed to correspond to saiddivided regions; and causing an incident light beam to be incident onsaid cell, diffracted light components emerging from said dividedregions of said cell being received by said light-receiving elements,thereby reproducing information.
 9. An information reading method for anoptical information recording medium according to claim (8), whereinbeam-like light is caused to be incident as the incident light.
 10. Anoptical information recording medium according to claim 1, wherein anintensity of a diffracted light component is coded based on thefollowing equation as a ratio of the line width to the grating pitch ofsaid diffraction gratings: ##EQU3## wherein η is a diffractionefficiency (a value of 0 to 1), r is a depth of the diffractiongratings, l is the line width, d is the grating pitch, θ is an angle ofincidence of reproduction illumination light, and λ is a wavelength ofthe reproduction illumination light.
 11. An optical informationrecording medium comprising:a planar substrate; at least one celldisposed on said planar substrate, said at least one cell having aplurality of diffraction gratings; and n regions included within said atleast one cell, with each of said regions encompassing at least two ofsaid plurality of diffraction gratings and being used to store a bit ofbinary data, with n being an integer equal to or greater than two. 12.An optical information recording medium according to claim 11, whereinsaid diffraction gratings of said at least one cell have at least oneof: (i) different azimuth angles, and (ii) different grating pitches foreach of said n regions.
 13. An optical information recording mediumaccording to claim 11, wherein said diffraction gratings of said atleast one cell have constant grating pitches.
 14. An optical informationrecording medium according to claim 11, wherein said diffractiongratings have different grating pitches.
 15. An optical informationrecording medium according to claim 11, wherein said n regions areformed by extending lines through a center of concentric circles, saidconcentric circles being aligned at a predetermined gap.
 16. An opticalinformation recording medium according to claim 11, wherein said nregions are formed by extending lines through a center of concentriccircles, said concentric circles being aligned at different gaps.
 17. Anoptical information recording medium according to claim 11, wherein saidat least one cell is a reflection type cell or a transmission type cell.18. An optical information recording medium according to claim 11,wherein an intensity of a diffracted light component is coded based onthe following equation as a ratio of line width to grating pitch of saiddiffraction gratings: ##EQU4## wherein η is a diffraction efficiency (avalue of 0 to 1), r is a depth of the diffraction gratings, l is theline width, d is the grating pitch, θ is an angle of incidence ofreproduction illumination light, and λ is a wavelength of thereproduction illumination light.